Interactions among rod cells will be studied by impaling two coupled rods with micropipettes. The effect of current injected into one rod upon the other rod will be observed when the retina is bathed in normal Ringer's and in Na ion free Ringer's. If injected current produces a change in membrane potential in the coupled rod when the retina is bathed in Na ion free Ringer's, then the hypothesis that the rods are electrically connected will be supported. An attempt will be made to measure light-induced changes in free (Ca 2 ion) by injecting a metallochromic indicator dye with high Ca 2 ion affinity into the rod outer segments. Changes in dye absorbance will indicate changes in the activities of the ligands that the dye binds.